In order for a driver to operate a vehicle safely he must know and have confidence in the stopping distance, and thereby the deceleration rate, of the vehicle in all environments. Drivers learn to judge this distance based on vehicle speed, road slope, road surface and load conditions.
Two conditions that can alter the driver's perception of a safe stopping distance are a non-functioning or partially functioning brake system or an unknown overload condition. As brakes do not wear linearly and can be affected by temperature, brake lining condition, moisture, adjustment, and mechanical problems, stopping distance can change over a short period. In addition, a vehicle may take on an unexpectedly heavy load, thus affecting stopping distance or vehicle deceleration rate.
Various systems for checking the effectiveness of vehicle braking systems are known. Common methods include visual inspection, mechanical devices (roller testers, plate testers), brake pressure gauges, and weigh scales to assure proper vehicle mass.
U.S. Pat. No. 5,299,452 (Caron et al.) determines vehicle braking effectiveness by first measuring engine torque to automatically calculate vehicle mass and then employing a complex averaging method to attempt to mitigate the effects of road slope, head winds, tail winds and the like. The accuracy of vehicle mass calculated by this method, using engine torque, is dependant on constant engine horsepower, transfer of horsepower to the wheels, fuel consumption, altitude, road surface and a level acceleration area. Changing vehicle conditions and variations in normal driving conditions such as uneven terrain, can significantly distort the calculation of vehicle mass using this method. In addition, estimating brake effectiveness based on level road conditions does not account for travelling up or down a slope. A brake effectiveness test that does not take into consideration road slope does not offer the real time feedback necessary to provide a true safety application.
It would therefore be desirable to provide a method and apparatus for providing feedback on vehicle brake effectiveness for vehicles that do not decelerate in the expected rate over a large spectrum of environments.
It would further be desirable to provide a method and apparatus of assessing vehicle brake effectiveness which takes into consideration travelling up or down a slope, differences in drag forces such as air friction and engine friction and engine brake engagement.
It would also be desirable to provide a method and apparatus of assessing vehicle brake effectiveness which includes a means of manually or automatically inputting the actual mass of the vehicle for use in calculating vehicle brake effectiveness.
It would further be desirable to provide a method and apparatus of assessing vehicle brake effectiveness based on a comparison with known vehicle deceleration rates for a known vehicle mass at 100% braking effectiveness.
It would also be desirable to provide a method and apparatus of assessing vehicle brake effectiveness based on a comparison with the minimum acceptable deceleration rate for the vehicle.
It would also be desirable to provide a method and apparatus of assessing vehicle brake effectiveness based on driver expected deceleration rates or on vehicle braking effectiveness history. Data collected on historical braking effectiveness can provide trends which may be critical in assessing real time vehicle safety and monitoring vehicle maintenance requirements.
A further desirable object is to provide an apparatus and method for alerting an operator to a deterioration in braking effectiveness or to a mass overload situation so that corrective action could be taken before the problem becomes critical.
It is also desirable that a method and apparatus be provided which will permit easy access to stored vehicle brake effectiveness data by certain authorized government regulatory agencies for the purpose of accessing vehicle safety.
While other methods of assuring effective braking for the main purpose of driver feedback and safety have a certain degree of efficiency in certain environments or braking areas, they do not provide the advantages of the improved methods and apparatus of the present invention as hereafter more fully described.